Abnormal vehicle dynamics can indicate a pending failure of a component of a vehicle. Abnormal vehicle dynamics have numerous causes. For example, a wheel defect can cause abnormal vehicle dynamics and be an indication of a pending failure of the wheel or a wheel-related operation (e.g., braking, suspension, and/or the like). Illustrative wheel defects that can cause abnormal vehicle dynamics include wheel flats, out of round wheels, wheel shelling, broken wheels, cracked wheels, broken springs, weak suspension dampers, and/or the like.
A wheel flat is a location on the tread of a railroad wheel which has become flat instead of curved. Frequently, a wheel flat occurs due to the railroad wheel being locked and sliding during braking. To this extent, a wheel flat is also often referred to as a “slid flat.” As it is flat, this section of the railroad wheel does not roll smoothly during use of the railroad wheel. In particular, each time the wheel flat rotates to contact the rail, it produces a significant impact. The impact can be detected in a number of ways, including wayside acoustic measurement, rail-based accelerometers, geophones, or optical measurement.
The impact resulting from a wheel flat is an important consequence of the presence of a wheel flat. Repeated impacts of a wheel flat cause drastically increased stresses to both the railroad wheel and rail, with vibration features that can transmit sufficient force to increase wear of other connected components. This damage can ultimately lead to a broken railroad wheel and derailment, and certainly reduces the usable lifetime of the railroad wheel as well as the rail. In passenger rail applications, wheel flats drastically increase noise and vibration, reducing ride quality. In addition, the noise and vibration can detrimentally affect systems outside of the railroad itself, either through simple noise pollution (increased noise in a neighborhood) or through the vibrations affecting sensitive systems for measurement of other quantities or of manufacturing delicate components (for example, a “fab house” for electronics may require extremely low vibration to function at all). There is thus a very strong incentive for both freight and passenger rail to detect and address wheel flats as quickly and reliably as possible.
Current art in wheel flat detection involves spacing multiple accelerometers a few feet apart along a pathway of roughly fifty feet. A typical installation will use a spacing of approximately two feet between adjacent accelerometers, thus using twenty-five accelerometers per side (a total of fifty accelerometers). The spacing is determined by the “damping” of the signal along the rail. The basic approach relies on an assumption that with a long line of spaced accelerometers, the wheel flat will rotate to the rail and cause an impact close enough to one of the accelerometers to be detected even over the noise and vibration caused by the passage of the train.
Similarly, there are systems that use an array of strain gauges located along a section of rail corresponding to at least one full revolution of a typical wheel. These systems detect the sharp peaks of strain caused by a wheel flat “hammering” the rail beneath it. Because of the varying strain of normal operation, these peaks can only be reliably detected at higher speeds, as low-speed operation masks the signal.
The current art is limited in several areas. First, depending on many conditions, the wheel flat may need to impact very close to an accelerometer or strain gauge to be reliably detected. As a result, simple geometry of rotation may lead to a flat rolling completely through the system without detection. Second, because the system must deal with powerful and variable noise from the train passage, only strong signals can be detected, which correspond with wheel flats above a certain size. As a result, smaller flats, which still can be significant in their potential to cause greater damage to the rail and railroad wheels as well as reducing fuel efficiency, go undetected. Third, because the strength of the impact signal is directly related to the speed of the train, current art systems are generally useless for trains traveling below about thirty miles per hour (about fifty kilometers per hour). As a result, current art systems cannot be successfully utilized at the entrances to railyards where the wheel flats could be immediately remedied if detected. Fourth, because the noise generated by a moving train increases drastically with speed, there is also an effective upper limit for the current-art systems of about sixty miles per hour (about one hundred kilometers per hour). Overall, current art systems have a detection rate (of the flat spots they can be expected to detect) of about eighty percent.
In addition, current art systems require sampling the accelerometers at relatively high rates of speed—over ten kHz per unit. As a result, the total data volume can easily exceed megabytes per second. Current art systems often process the data using fairly time-intensive methods, which preclude real-time detection in most cases. Other approaches attempt to utilize thresholding to identify wheel flats. However, these approaches do not provide a reliable solution.